1. Field of the Invention
This invention relates to motion systems, including goniometers, for rotating, translating, tilting and/or rocking a sample, for example, in a Double Crystal X-ray Diffractometer (henceforth DCD). More particularly, this invention relates to a goniometer used in a mapping DCD, where rocking curves are measured at a large number of locations on semi-conductor wafers or in other instruments requiring a eucentric mapping goniometer.
2. Description of the Prior Art
It is known to have mapping DCD's that use x-y stages added to a sample motion system that performs sample tilt alignment and rocks the sample so that a rocking curve may be recorded at a large number of positions on the sample to produce an X-ray map of the sample. Since the axis about which the rocking motion occurs is on the plane of the sample and must pass through the particular sample position upon which an X-ray beam coming from a first crystal impinges, previous DCD's rock the sample, sample holder and the x-y stages about that axis. After a rocking curve is recorded at one sample position, the x-y stages move the sample so that a new measurement point on the sample is positioned relative to the X-ray beam and a new rocking curve is recorded at that position. This procedure is continued until an X-ray map of the sample has been obtained. Since the x and y stages as well as the sample and sample holder are rocked each time a rocking curve is measured, previous motion systems or goniometers are relatively slow and can be relatively expensive. For example, when a sample is such that thousands of measurements are required to map it at high spatial resolution, several hours or even days may be required to map the entire sample (see the paper by Halliwell, et al. entitled "Assessment of Epitaxial Layers by Automated Scanning Double Axis Diffractometry", published in the Journal of Crystal Growth 65 (1983), pages 672-678 and the paper by Macrander, et al. Entitled "X-ray, Photoluminescence, Stoichiometry, and Thickness Mapping of In.sub.1-x Ga.sub.x As.sub.y P.sub.1-y ", published in the Journal Electrochemical Society, Vol. 138, No. 4, in April, 1991, at pages 1147-1153.